The present invention relates to optical aperture multipliers and, in particular, it concerns an optical aperture multiplier that includes a rectangular waveguide, and near-eye displays and head-up displays which employ such aperture multipliers.
Optical arrangements for near eye display or head up display require large aperture to cover the area where the observer's eye is located (the eye motion box). In order to implement a compact device, the image is generated by small optical image generator having small aperture that is multiplied to generate a large aperture.
An approach to aperture multiplication in one dimension has been developed based on a parallel-faced slab of transparent material within which the image propagates by internal reflection. Part of the image wavefront is coupled out of the slab, either by use of obliquely angled partial reflectors or by use of a diffractive optical element on one surface of the slab. Such a slab is referred to herein as a one-dimensional waveguide in that it contains the image wavefront by internal reflection in one dimension. In the plane of the slab (i.e., of the slab surfaces), the image must be collimated so as to maintain image quality across the waveguide.
The slab-propagation approach is quite suitable for a second stage of aperture multiplication, where the slab is deployed opposite the eye of the observer (like a glasses lens for near-eye displays, or a window for larger head-up displays) and forms the final output surface from which the image reaches the eye. This approach is however non-optimal for a first stage of multiplication, where the requirements for width of the slab compared to the width of the image wavefront add bulk and weight to the device.